Grinding mill



March 21, 1944. L. DOTZER GRINDING MILLS Filed May 28, 1941 7 Sheets-Sheetl lNVENTO R Y IED 007259 ATTORN EY March 21, 1944.

L. DOTZER GRINDING MILLS Filed May 28, 1941 7 Sheets-Sheet 2 LEON/1RD D0 TZEE lNV ENTOR ATTORNEYS March 21, 1944. L. D OTZER GRINDING MYILLS Filed May 28, 1941 7 Sheets- Sheet 3 INVENTOR ATTO R N EY March DQTZER GRINDING MILLS Filed May.28, 1941 7 Sheets-Sheet 4 INV ENTOR 150M120 Dorzzk' ATTORN EYS March 21, 1944. L. DOT ZER GRINDING MILLS Filed May 28, 1941 7 Sheets-Sheet 5 R 5 RH Y m m mw m V QM Y .B v Wm March 21, 1944.

L. DOTZER GRINDING MILLS Filed May 28. 1941 7 Sheets-Sheet 6 INVENTOR LEOHHED Do 725/? ATTORNEY March 21, DOTZER GRINDING MILLS Filed May 28, 1941 7 Sheets-Sheet '7 INVENTOR ZfONA'ED D0 HER r ATTORNEYJ Patented Mar. 21, 1944 UNITED STATES PATENT OFFICE GRINDING MILL Leonard Dotzer, Milton, Mass. Application May 28, 1941, Serial No. 395,591

5 Claims.

This invention relates to improvements in reducing and grinding mills of those types and for the purposes, of the mills disclosed in U. S. Letters Patent No. 2,176,892, issued to Leonard Dotzer et al. on October 24, 1939, and also of those mills disclosed in my pending application, filed August 19, 1939, under Serial No. 291,025. Both in the pending application and in the'p'atent, various mills have been shown and described, wherein three coaxially aligned grinding stones are employed in face to face relationship, thus providing that material may be ground, or reduced, between the coacting surfaces of the opposite surfaces of the central stone and inner surfaces of the stones at opposite sides of the central stone.

More particularly, the present invention relates to improvements in mills of the above stated kind, designed for the initial crushing of cocoa nibs and the subsequent fine grinding of the particles.

The objects of the present invention are mainly concerned with the provision, in mills of the above character, of hydraulic means for equalizing and regulating the grinding pressures, as applied by the stones at upper and lower sides of the middle stone against the middle stone.

Explanatory to the present invention, it will here be stated that in those mills featured in my above mentioned pending application, employing three, coaxially arranged stones and providing for the grinding of material at both sides of the central stone, the central stone is designated as being of the floating type; that is, it does not have fixed mounting with respect to it vertical movement, but adjusts itself automatically between the top and bottom stones in accordance with the applied grinding pressures, and the pressure of springs which are employed to act against the stones to efiect a yielding application of the grinding pressures.

In such an arrangement of stones and pressure applying springs, it is a difficult matter to establish and then to maintain any definite grinding pressure for an extended grinding period or to maintain equalized grinding pressures on opposite sides of the middle stone. This is due partly to the manner of mounting the stones and influences of the weight of the various stones, as well as to the fact that the tension of themessure applying springs will vary or change with use and with their change in temper. Thus, to maintain equality in grinding pressures at opposite sides of the middle stone, it is required that special precautions be taken, that frequent tests be made, that spring pressures must be accurately measured and adjustments rnade accordingly.-

Furthermore, unequalpressures at upper-and lower sides of the middle stone that result from the influences of weight of the stones, requires that a lesser feed of material must be applied to the grinding space at the top surface of the middle stone than to the lower surface. This naturally results in a loss of grinding efficiency in the mill.

In view of the above difficulty, and for other reasons which will later become apparent, it has been the principal object of this invention to provide a mill construction employing three horizontal, axially arranged stones, and wherein equalized grinding pressures at upper and lower sides of the intermediate or the central stone can be obtained in a satisfactory and practical manner by economical and inexpensive means to bring about a higher operating efficiency in the mill, due to the fact that material to be ground may be fed to both sides of the middle stone in equal amounts and ground at the same pressures.

It is a further object of the present invention to provide novel means for effecting an equalization of pressure, embodying hydraulic jacks that are arranged to act against the upper and lower stones in a manner whereby to urge them toward the middle stone at pressures that will either compensate for or not be influenced by the effect of the weights of the stones.

It is a still further object of this invention to provide a grinding mill of the character above stated, using three horizontal, coaxial stones, and wherein the central stone is rotatable but is held against vertical movement during operation, providing that the opposing pressure, applied by the grinding stone, whether at the top or at the bottom side thereof, will not alter or afiect the grinding pressure applied by the stone at the opposite side.

Another object of this invention is to provide novel devices whereby the upper stone, when not in use, may be held suspended and in spaced relationship from the middle stone, and. manually or automatically controlled means whereby these suspending devices may be simultaneously released from the stone for its functional operation.

Another object of the invention is to provide a mill using segmental stones and a practical means for bringing the segments of any stone to a common level.

Still further objects of the invention reside in the details of construction of parts, in their combination and in their mode of operation, as will hereinafter be fully described.

In accomplishing these and other objects of the invention, I have provided the improved details of construction, the preferred forms of which are illustrated in the accompanying drawings, wherein Fig.1 is a vertical, sectional view of a mill embodying the present invention, as seen in the vertical, axial plane of the grinding stones.

Fig. 2 is a top or plan view of the same; a part being broken away for better illustration.

Fig. 3 is a horizontal section on the line 3-3 in Fig. 1, particularly illustrating the base frame.

structure.

Fig. 4 is a horizontal section, taken on line 4-4 in Fig. 1, particularly showing the supporting frame for the upper grinding element.

Fig. 5 is an enlarged sectional detail taken on the vertical plane of line 5-5 in Fig. 4.

Fig. 6 is an enlarged sectional detail taken on line 6-6 in Fig. 8, illustrating the means for adjusting and securing one of the stone segments in place in its frame.

Fig. '7 is an outer edge view of the stone, showing the securing plates.

Fig. 8 is a plan view of the central grinding element.

Fig. 8a is a sectional detail of one of the breaker plates.

Fig. 9 is a vertical sectional View showing the relationship of grinding elements in the machine.

Fig. 10 is a cross sectional detail of the wheel structure as seen on line lfll0 in Fig. 8.

Fig. 11 is a view diagrammatically illustrating a hydraulic system for the pressure applying and supporting jacks for the upper and lower grinding elements.

Fig. 12 diagrammatically shows a hydraulic system for a mill having a floating center stone.

Briefly described, the present mill comprises a frame structure wherein three horizontally disposed grinding elements, or stones, are arranged in coaxial alinement; the central element is rotatably mounted and is driven by a gear pinion meshing with a ring gear which encircles and is fixed to the element. The upper and lower elements are held against rotation and are adjustably spaced from the upper and lower surfaces of the central element. Conventional means is provided for feeding the material to be ground between the opposed grinding surfaces of adjacent elements, and means, according to this invention, is provided for regulating the grinding pressures applied through the mediacy of the stones. Ground material is centrifugally discharged from between the coacting surfaces of the grinding elements to a receiving trough and is delivered from the machine.

' Referring more in detail to the drawings- In its present illustrated form of construction the present machine comprises a base frame structure which, as noted best in Figs. 1 and 3, includes a central horizontally disposed metal ring I and a larger, outer ring 2; this latter ring being formed from an angle bar and being disposed concentrically of the ring I. .The two rings, i and. 2, are supported substantially at the of 120; each leg frame comprising inner and outerupright channel members 3 and 4, joined across their upper end portions by horizontal bars, as designated at 5. The lower ends of the outer channel members 4 are fixed to an encircling ring 6 that is disposed flatly uponand secured to a bottom or bed plate 8. The upper end portions of the channel members 3 and 4 of each leg frame are fixed, by welding or otherwise,

respectively to the central ring I and to the ring 2. g v The frame structure of the machine also ineludes an upper, or top section, as shown best in Fig. 2. This comprises a horizontally disposed central ring [0 about which a triangular, horizontal frame is symmetrically disposed; this frame comprising the three channel beams ll joined at their ends by blocks l2 andsupported from the ring In by interposed web plates l3. The beams II are joined and braced across the angles by vertical, spaced plates 14-44, thus with the beams ll, providing a rigid, three sided frame section.

This upper frame section, as presently will be understood, mounts the hydraulic jacks whereby the grinding pressure of the upper stone is regulated.

The upper section of the frame structure is supported rigidly from and in spaced relationship above the base frame structure, by three vertical columns or posts 15. These posts are fixed at their lower ends in bearing blocks or brackets I6 that are secured to the outside of the base frame at the location of the supporting legs. At their upper ends, the posts likewise are fixed in bearings formed by the blocks !2 and caps l2a. that are applied and bolted to the blocks over the post ends. These three posts are shouldered near their ends to seat firmly against the faces of the bearings. Nuts, as at H, are threaded onto the ends of the posts to rigidly secure the parts.

Fixedly supported Within the central ring II! of the upper frame section, is a three-armed spider 20, and likewise rigidly supported within the central ring I of the base frame section, is a similar spider 2|. Mounted by these two spiders at the axial center of the machine, is a vertical shaft 22 which is the supporting axis for the central grinding element presently to be disclosed. The upper end portion of the shaft 22 is revolubly mounted in a bearing 23 at the center of the spider 20 and the lower end portion is contained in and is supported by anti-friction, double thrust bearings as at 24 contained in a housing 25 formed at the center of the spider 2!. A downwardly facing shoulder 26 formed about the lower end portion of the shaft 22, engages against the top bearing 24 to support the shaft against downward movement.

Fixedly mounted on the vertical shaft 22 is the central grinding element of the mill which, for convenience, as considered in its entirety, will hereinafter be referred to as the central grinding wheel. This wheel comprises a metal frame structure which mounts breaker plates and grinding stones on its upper and lower faces, as later will be more fully described.

The wheel frame is formed with an elongated, central hub bearing 21 which is bored to receive the shaft 22. About the central bore is anfannular passage 28 divided, as noted in Fig. 8, by

a. plurality of vertical webs 29' forming a plurality of openings that extend vertically through the hub for the feeding. of material that is to be" ground, to the lower side of the Wheel, as. presit being understood that the wheel is coaxial of shaft 22 and that the wheel hub 21 is so fixed 1 or keyed on shaft 22 that no vertical movement of thewheel is possible'under application of grinding pressures either at top and bottom sides thereof.

Mounted centrally upon the frame structure of the central grinding wheel is a flat, annular breaker plate or disk 34'. This has a diameter approximately half that of the wheel and has a central opening. The peripheral portion of the disk 34, about this central opening, rests upon and is fixed to an annular shoulder 21' formed about the upper end portion of the hub 21 of the wheel, and this central opening conforms in diameter to that of the annular passage 28-, and thus it does not interfere with feeding of material to or the downflow of material through the annular passage. About its outer periphery, the breaker plate 34 rests upon and is secured toa ring 35 that is mounted on the radial arms, or spokes 29, of the wheel.

Supported by the spokes 29 of the wheel, about the breaker plate, is an annular floor plate 33 surrounded by an upstanding ring 36 also fixed to the wheel. Mounted upon the plate 33 and confined between the rings 35 and 36 are the segments of a grinding stone 3-1 which forms the top grinding surface of the central wheel, and it will be observed, by reference to Fig. 1, that the diameter of this stone, which is concentric of the wheel, is such as to leave an annular space 33 between the ring gear flange and the outer periphery of the stone for a downflow of ground material, or chocolate liquor, as it is exuded from between the coacting surfaces of the top and central stones.

It will here be explained that the ooacting breaker plates of opposing elements as used in the present machine, are not primarily for grinding purposes, but rather are for the crushing or breaking up of the cocoa nibs into pieces of proper size for their passage between the coacting surfaces of opposed grinding stones for a finer reduction.

To best accomplish its purpose, the grinding surface of each breaker plate is formed with alternating ridges and grooves which may be patterned according to the showing in Fig. 8, wherein the plate is divided into segmental sections of equal extent and the ridges and grooves as applied over the area of each segment are parallel and lead toward the periphery of the disk for centrifugal delivery of crushed material. It will be further understood that the patterned surfaces of opposed breaker plates, due to rotation of the center wheel, operate on the material that is fed between them, to crush and then advance the crushed material to the surrounding grinding stones,

In Fig. 8a, I have shown an enlarged cross sectional view of the grooved surface of a breaker plate wherein the grooves are designated by reference numeral 39 and the ridges by numeral 39'. The walls of the ridges and grooves are evenly rounded to facilitate the crushing operation without clogging. These plates are of cast steel or cast iron with their patterned surfaces chilled to great hardness. To secure the breaker plate 34 in place, it is tapped about its inner and outer peripheries and anchor screws 40 extend therethrough and into the hub and ring 35, as noted in Figs. 8 and 9.

The stone 3'! is divided into a plurality of segments and these segmental portions 3'laare set in cement on the top side of the center wheel. on plate 33 between the rings 35 and 36, and

are adjusted and secured in place by means stone.

shown best in Figs. 6, *7 and 8, wherein it is noted that for each stone segment, four leveling screws 42 are threaded upwardly through the metal floor plate 33 to supportingly engage with the segment; these screws being adjustable for the purpose of leveling the individual segments and to bring them all to a common level and their top surfaces substantially flush with the top surface of the breaker plate: 34 prior to the setting of the cement. These adjusting. screws are headed at their lower ends and their upper ends engage the stones at locations within what may be considered their corner areas, in order to provide firm bearing for the segments. After the stones have been properly leveled in the wet cement, they are left still until the cement has set, then the screws are pulled back to be free of contact with the stones as a precaution against their breaking the stones.

It is also to be observed that each segment 31a of the stone is held in place by three anchors 45 that are attached to the floor plate 33 and which extend upwardly and have flanges 4% turned inwardly at their upper ends to project into laterally opening sockets 46 provided in. the inner and outer side surfaces of the stone segments, as will be understood best by reference to Figs. 6 and 7. It is to be noted that there are twospaced anchor plates 45 at the outside of each stone segment, securely welded to the floor plate 33, with their upper end portions 45 turned inwardly and cemented in the sockets 46 and that there is one, centrally located anchor at the inside of the segment. This latter anchor comprises a horizontal flange 45a cemented in the stone socket and mounted by a bolt shank 436, see Figs. 6 and 8, applied within an inwardly opening notch 47 in the inner edge of plate 33. A nut 48 is applied to the lower end of the shank and is drawn tight after the cement has set.

In mounting. these stone segments 31a, they are placed in position, brought to proper level by adjustment of the supporting screws 42, and then the spaces are cast out with cement, that is, they are grouted into place. The anchors are embedded in the cement at the same time while the inturned flanges of the anchors 45 are cemented in their respective sockets 46; it being understood that the sockets are oversize to more easily receive the inturned flanges and to provide that they might be completely embedded.

If any stone segment becomes cracked, or dam.- aged, the anchor at the inside may be removed for release of the stone and this provides for removal of the stone segments for replacement.

The bottom side of the center wheel likewise mounts a downwardly facing breaker plate 34!) and segmental grinding stone 31b like the corresponding parts at the top side of the wheel. These latter parts cooperate in the same manner with the corresponding parts of a bottom grinding stone, and for the same purpose as those at the top side of the wheel coact with the. upper Thus, in view of the description previously given of the breaker plate 34 and stone 31, as applied to the top side of the center wheel, it is not thought necessary that it be repeated with reference to the corresponding parts as applied to the bottom side of the wheel, and it will be understood that the foregoing description as it concerns the breaker plate 34 and stone segments 31, and their associated mounting means, applies equally to these parts, 34b and 311), on the under side of the wheel. 'The breaker plate 34b is fixed to the lower end of wheel hub 2! and to a ring 351) corresponding to ring 35, while the. severalsegments of the stone 31b are suspended from a floor plate 361) that corresponds to the upper floor plate 33. v

To drive the center wheel, I have provided a verticaldrive shaft 50, revolubly mounted in bearings and 52 carried by frame brackets 53 and 54 secured to the upper and lower sections of the main frame. Keyed on this shaft 5!] is a gear pinion 55, operating in mesh with the gear teeth of the center wheel, and near its lower end hearing, .a pulley wheel 56 is keyed on the shaft, about which a driving belt, as indicated at 51 in Fig. 3, may operate to drive the shaft 58 and thus r0.- tate the .center wheel. An electric motor, as at 58 in Figure 3, may be used to furnish power for operating the mill, or any other suitable driving means might be employed.

Now, describing the lower grinding stone, and its mounting means: This, as noted in Fig. 1, comprises a vertically adjustable, but non-rotatable frame structure including a central, horizontally supported ring 60, from which three equally spaced radial arms 6| extend. At their outer ends, these arms mount guide hearings, or blocks 62 which are slidably fitted to the vertical post I5 to permit vertical adjustment of the frame while holding it against rotation.

Supported within the ring Bil is a spider fram 63 which includes a central hub portion 64 through which shaft 22 extends. This hub has an upwardly rounded top surface 65 spaced somewhat from the lower end of hub 27. Supported upon this spider hub 54 is an annular breaker plate 66 of the same kind or character as the breaker plates 34 and 34b previously described. The plate 65 is fixed to the spider 63, which, in turn, is fitted about its periphery for vertical adjustment in ring 60, and is held against rotation and for coaction with the breaker plate 34b on the bottom side of the center wheel.

The vertical adjustment provided for the spider 63 is in order that the breaker plate 65 may be adjusted toward or from the breaker plate 3 31) for finer or coarser initial breaking of the material that is to be ground. The peripheral ring 63 of the spider frame has threaded mounting upon three equally spaced adjusting screws 83 that are rotatably fixed in bosses 84 that are bolted or welded onto the inside of ring 60, as shown in Fig. 8. After an adjustment of the spider has been made, it may be secured by the tightening of set screws 83' that are threaded through the spider ring to holdingly engage the inner face of ring 60.

Supported upon the radial arms 6! of the frame structure for the lower grinding element, is a floor plate 61, and fixedly mounted on this, concentrically of the shaft 22, are spaced rings 68 and 59, forming a trough between them. Also, the ring 60 is welded to plate 67 to fix them solidlytogether. The lower grinding stone TI is also in segments and is located between the ring Biiand'ring 63, and the individualsegments are anchored to plate (Win the same manner as was previously described with reference to the anchoring of the top stone to plate 33. These segments, like those of the top stone, are set in cement, as'has been indicated. The top surfaces of the several segments of stone]! lie flush with the top plane of the breaker plate 56. I

The trough it which surrounds the lower stone and which is formed between the spaced rings .69 and 63, serves as a collector forthe ground ri iaterial exuded from between the grinding surfaces at upper and lower sides of the center wheel; the trough being concentric of the stones and fitted closely about the lower stone. Aidelivery chute 13 leads from the trough as noted in Fig. 1 at the left-hand side. f The frame structure provided for support of the upper grinding element comprises a central ring 14 from which three radial arms 15 extend. These arms mount guide bearing blocks '16 at their outer ends which are fitted slidably to the posts 15 for vertical adjustment of the frame while holding it against rotation. Encircling'the ring '14 and mounted by the radial arms 15, is a base plate ll from which the upper grinding stone l8 is suspended. This stone likewise may be made in segments, each segment to be secured in place by anchors as previously explained, and set in cement, or the like, to give greater solidity. The segments of stone 18 would be flush with the surface of a breaker plate or disk that is mounted on the under side of a spider frame 8| slidably fitted for vertical adjustment within the ring 14, and is in opposed relationship to the breaker disk 34 of the central wheel.

The adjustment of the spider frame 8| for a adjustment of the breaker plate 89 toward or from the plate 34 is by means corresponding to those for the lower plate. Set screws 83a are rotatably fixed in bosses 84a bolted to the ring 14 and have threaded connection with the ring 8 i that constitutes the base of the spider. Lock-- ing bolts 83' also are used to secure the spider-at its diiferent positions of adjustment. These extend through the ring 8| and may be tightened against the ring M. The breaker disk 80 has a central opening 82'that is concentric of shaft 22 and somewhat greater in diameter than theopening in breaker disk 34. V I It will be noted by reference to Fig. 1 that a cylindrical, upwardly extending sleeve 85 is mounted at its lower end upon disk 34 about the central opening. This sleeve extends upwardly slightly above the level of the top of ring 14, in Fig.1,and is open to receive material from a feed pipe, that is to be ground between the coacting surfaces of the middle and bottom stone; this sleeve ineffect is a continuation of the annular passage 28, Also, there is a similar sleeve 8'! fitted at its lower end in the central opening of' disk 86, and this also is adapted to receive material into its upper open end for delivery through the central opening of the disk 80. Feed devices have been designated at 89 and 89 in Fig. 1 with delivery spouts 9i! and 90' leading to the. upper ends of the two sleeves 85 and 86, and the flow of material therefrom to the grinding surfaces is a indicated by the arrows in Fig. 9.

Ground material will be exuded from between the grinding surfaces of the central and upper stones in the form of a thick paste and will fall into the annular space 38 just within the ring gear. Aplurality of paddles, as at 9! are fixed to the stationary upper'stone frame, which .ex tend into the annular channel as a means of wiping the liquor from the periphery of the rotating central stoneto cause it to drop through into the trough 'lfi'that is directly below. Also, a plurality of similar paddles 9'! are fixed to the center r In order that the upper stonemay, whenleft idle'for some time, be held in suspension, spaced from the top side of the middle stone, I have pro- ,vided three suspending hooks c4 pivoted in, the I top frame, as noted in Fig. 1, and adapted to holdingl-y engage with cross pins 95 in the top stone supporting frame. Each hook has a lateral arm 96 operatively connected with a solenoid 91 in such manner that upon energizing the solenoids, all hooks will be simultaneously released from their pins and the stone will be allowed to lower. When the stone is lifted to a predetermined height, it causes the hooks to automatically engage their respective pins for suspension of the stone.

Assuming the parts to be so constructed and assembled, it will be understood that, with the central wheel rotatably driven and the upper and lower stones held against rotation, material that is fed between coacting surfaces of the breaker plates and stones of the central and upper and lower stones will be crushed and ground. Furthermore, the extent of grinding will be in accordance with the feed and the degree of pressure of coacting surfaces against the material.

As previously explained, it is desirable that these pressures at upper and lower sides of the central wheel be the same, and this is-accomplished in the present instance by means that aifords a desired pressure and at the same time compensates for the variances that are due to the weight of the upper stone which tends to increase its pressure and that of the lower stone which similarly tends to decrease its pressure.

The lower frame structure by which the lower breaker plate 66 and the stone 1! are carried is vertically movable and guided by the posts I5,

and is adjustably supported through the mediacy of three single acting hydraulic jacks each designated by reference character IE5. These jacks are supported vertically in the leg frames whereby the machine is supported. Each jack comprises a hydraulic cylinder I92 and a piston I03 from which a vertical rod I64 extends upwardly for supporting contact with the floor plate 61 within one of the radial arms 6i fixed to and extending from the ring 61] and constituting a part of the stone mounting frame. The arrangement provides that by extending and retracting the piston rods, the supporting frame structure for the lower stone will be raised and lowered accordingly.

Likewise, fixedly mounted by the upper frame structure carried by the upper ends of the shafts I5, are three double acting hydraulic jacks IIU, each with a piston rod I I I extending downwardly and support-ingly connected at its lower end with one of the radial arms of the upper stone mounting frame. The extent of application of hydraulic pressure medium to these sets of upper and lower jacks determines the grinding pressures at which the top and bottom stones are urged against or toward the central stone, and it can be understood that the weight of the top stone will ordinarily increase its pressure accordingly while weight of the lower stone will likewise decrease its eifectiveness. Therefore, it is desirable that thepressure be controlled and that the effect of these weights be compensated for to such extent that the efiective grinding pressures be equalized at upper and lower sides of the middle stone.

In Fig. 11, I have diagrammatically illustrated a hydraulic system for the present type of machine, having the middle stone held against upward or downward movement for independent applications of pressure at the upper and lower sides. In this system, it is the intent that the pressures for upper and lower stones be individually controlled through the use of pressure control valves and indicating gauges in the pressure lines. In the system, as herein illustrated, a suitable pump IIB, driven by motor H9, operates to draw a liquid pressure medium from a storage tank I20 through a pipe H8 and to deliver it through a pipe I20 to a safety relief valve 153 of a type whereby a desired maximum pressure may be set. A pipe I 5| leads from valve I50 to a four-way valve I52 controlled by a valve lever I52a that is adjustable from a closed position P to positions P and P From the valve I52, pipes I53 and I54 are extended to deliver the pressure medium in accordance with the setting of the lever I52a to the upper and lower ends respectively of the jack cylinders I10 and to the lower ends of jack cylinders ma,

The pressure medium is supplied to the lower ends only of cylinders I00, and this is through a pipe .I 56 that leads from pipe I53 to a pressure reducing valve I51, from which valve a pipe I56 leads to supply the various jacks Illll with the mediumat a pressure that is in accordance with the pressure setting of valve I51.

7 The pipe I53 likewise has a pressure regulating valve I51a interposed therein for control of pressures delivered to the jacks I I0, and the valves I51 and I5'Ia, respectively, have circulating connections I553: andIEBx leading to the pipe I55. Also, in those pipe connections between pipe I54 and lower ends of the various jack cylinders H0, and in the pipe connections between the supply pipe I56 and lower ends of jacks I00, are flow restriction fittings I60. The cylinders I00 are equipped with drain connections at their upper ends into a pipe -I 56:1: which leads back to tank I26. This is to take care of any leakage past the jack pistons.

.By use of the valves I51 and I51a, the pressure of the hydraulic medium at the outlet sides may be regulated and maintained Within a wide range so long as the inlet pressure is somewhat above the outlet pressure. These Valves will drain the system at the low pressure side as soon as the oil flow is stopped at the inlet side.

Assuming the pressure system to be as above described, it is understood that with relief valve I51 set at a desired maximum pressure, the control lever of valve I52 is adjusted to position P and the pump started. The valve I52, in this setting, will direct the pressure medium through pipe I54 into the lower chambers of the upper jacks i It] and lift their pistons slowly on account of the flow restriction fittings I59. As soon as the suspension hooks 94 are relieved of their loads, and the hooks released, the valve lever I52a is shifted to position P and the oil flow will now be divided into the two pipes I53 and I56. On passing through reducing valve I51a which has been set for the desired pressure, the pressure medium will enter the top chambers of jacks III) and actuate their pistons downwardly, slowly on account of flow restriction fittings Hit. By the pipe connection I54, the pressure medium from the lower chambers of jacks II!) will be led to valve I52, thence back to tank I211 through a pipe connection I58. In a like manner, the pressure medium from pipe connection I5$ passes through the reducing valve I51, which has been set for a desired grinding pressure, into the lower chambers of When it is desired to shut down the system, the valve lever I52a is moved back to position P The oil entering the lower chambers of jacks IIU will press their pistons upwardly, thereby displacing the oil from the upper chambers through pipe I53 and reducing valve I51a, and through the four way valve I52 into drain line I58 to storage. The weight of the bottom stone will force the medium from the lower chambers of jacks I through valve I51 and valve I52 to the drain I58. The pipe connections I531: and I563: make it possible to maintain a constant circulation through the reducing valves I51 and I5'Ia, which is necessary in order that these valves, in operation, may maintain an even static pressure on the low pressure 5 side of the valves and to take care of possible oil losses through piston leaks.

In the above system, for individual pressure applications, it will be understood that the gauge readings for top and bottom stones would not show the same because of the effect of the weights of the stones. Therefore, to make it possible for both gauges to read the same when like grinding pressures are being applied, it is necessary to provide specially calibrated dials for the two gauges which would take into consideration the influences of the weights of the stone. Thus to allow the mill operator to always set the gauge pressures alike for the top and bottom grinding surfaces, which would simplify the mill operation.

In Fig. 12 is illustrated in a diagrammatic way, a hydraulic pressure system for mills in which the center stone is of the floating type, as differentiated from being fixed. For this floating arrangement, single acting hydraulic jacks IOU are used to lift the bottom stone and to provide the desired grinding pressure. The pressure medium in this instance is supplied from tank I by pump I I8, which delivers it through a relief and pressure adjusting valve I10 like valve I previously described, and from valve I10, it passes through pipe I12 and four-way valve I13 to pipe I 14 whereby it is delivered to the various jacks. The valve I13 has a drain pipe connection I18 to the tank, and when the valve is adjusted for release of the pressure, the jacks drain their pressure medium, and the stones will separate by reason of their own weight. Pressure of the top stone is effected through the use of adjustable spring I15.

In this arrangement, the higher grinding pressure of the top stone due to its weight, may be counteracted by feeding more liquor to the lower stone.

Having thus described my invention, what I claim as new therein and desire to secure by Letters Patent isl. A mill of the character described comprising a series of three horizontal stones in face to face opposition for the grinding of material between them, means for feeding material between 0pposed grinding surfaces at opposite sides of the middle stone, means for supporting the middle stone at a fixed level for rotation, means for rotating the middle stone, means supporting the outer stones against rotation and for adjustment from and toward the middle stone, and hydraulically powered means for the adjustment of the upper and lower stones; said means comprising a hydraulic circuit, means operable to maintain flow of a hydraulic pressure medium therein at higher than grinding pressures, hydraulic jacks supporting the upper and lower stones, pressure applying connections between the hydraulic circuit and said jacks, a control valve incorporated in said connections and operable to effect the application of pressure medium to the jacks to move the stones from or toward each other, and pressure relief valves in the connections between the jacks andcontrol valve for determining the effective grinding pressures.

2. In a mill of the character described, a set of three horizontal stones in face to face opposition for the grinding of material between them, means I supporting the middle stone at a fixed level, means mounting the upper and lower stones for adjustment toward and from the middle stone, means for causing relative rotation of the stones, means for feeding material between the'stones for grinding, and a hydraulically powered means for adjusting the stones; said means comprising a plurality of hydraulic jacks for adjusting each of the adjustable stones, a hydraulic pressure circuit, means for maintaining a predetermined hydrostatic pressure therein, a control valve connected with the said pressure circuit, pressure lines from the said control valve to the pressure sides of the jacks, return connections from the lifting sides of the jacks to the control valve, pressure relief valves in the said pressure lines, relief connections from said pressure relief valves to the said control valve, and a return connection between the control valve and the pressure circuit; said control valve being operable to direct the pressure medium from the pressure circuit to'either side of the jacks.

3. In a mill of the character described, a main frame structure, a set of horizontally disposed stones mounted therein for the grinding of material between them, means for the delivery of material between the stones for grinding, means for supporting the lower stone at a predetermined grinding level, means for causing relative rotation of the stones, means for lifting the top stone clear of the lower stone for shut-down periods, spring pressed hooks pivoted in the frame and adapted to be functionally engaged by the stone when it is lifted to shut-down position for the positive support thereof, and means common to all hooks to effect their simultaneous release from the stone.

4. A mill as recited in claim 3, wherein the said last mentioned means comprises a solenoid associated with each hook adapted, upon energization, to actuate the hook to disengaged position, a circuit for the solenoids and a switch in the circuit.

5. In a mill of the character described, a set of three horizontal stones in face to face opposition for the grinding of material between opposed surfaces, means for supporting the middle stone at a .fixed level, means adjustably mounting the upper individual distributing circuits leading from the control valve respectively to. supply the sets of jacks of upper and lower stones, pressure regulating valves in the distributing circuits whereby predetermined pressures may be maintained on the stones at opposite sides of the central stone,

by-pass connections from the last named valves to the circuit.

LEONARD DOTZER. 

